/net/atm/pppoatm.c

  1// SPDX-License-Identifier: GPL-2.0-or-later
  2/* net/atm/pppoatm.c - RFC2364 PPP over ATM/AAL5 */
  3
  4/* Copyright 1999-2000 by Mitchell Blank Jr */
  5/* Based on clip.c; 1995-1999 by Werner Almesberger, EPFL LRC/ICA */
  6/* And on ppp_async.c; Copyright 1999 Paul Mackerras */
  7/* And help from Jens Axboe */
  8
  9/*
 10 *
 11 * This driver provides the encapsulation and framing for sending
 12 * and receiving PPP frames in ATM AAL5 PDUs.
 13 */
 14
 15/*
 16 * One shortcoming of this driver is that it does not comply with
 17 * section 8 of RFC2364 - we are supposed to detect a change
 18 * in encapsulation and immediately abort the connection (in order
 19 * to avoid a black-hole being created if our peer loses state
 20 * and changes encapsulation unilaterally.  However, since the
 21 * ppp_generic layer actually does the decapsulation, we need
 22 * a way of notifying it when we _think_ there might be a problem)
 23 * There's two cases:
 24 *   1.	LLC-encapsulation was missing when it was enabled.  In
 25 *	this case, we should tell the upper layer "tear down
 26 *	this session if this skb looks ok to you"
 27 *   2.	LLC-encapsulation was present when it was disabled.  Then
 28 *	we need to tell the upper layer "this packet may be
 29 *	ok, but if its in error tear down the session"
 30 * These hooks are not yet available in ppp_generic
 31 */
 32
 33#define pr_fmt(fmt) KBUILD_MODNAME ":%s: " fmt, __func__
 34
 35#include <linux/module.h>
 36#include <linux/init.h>
 37#include <linux/interrupt.h>
 38#include <linux/skbuff.h>
 39#include <linux/slab.h>
 40#include <linux/atm.h>
 41#include <linux/atmdev.h>
 42#include <linux/capability.h>
 43#include <linux/ppp_defs.h>
 44#include <linux/ppp-ioctl.h>
 45#include <linux/ppp_channel.h>
 46#include <linux/atmppp.h>
 47
 48#include "common.h"
 49
 50enum pppoatm_encaps {
 51	e_autodetect = PPPOATM_ENCAPS_AUTODETECT,
 52	e_vc = PPPOATM_ENCAPS_VC,
 53	e_llc = PPPOATM_ENCAPS_LLC,
 54};
 55
 56struct pppoatm_vcc {
 57	struct atm_vcc	*atmvcc;	/* VCC descriptor */
 58	void (*old_push)(struct atm_vcc *, struct sk_buff *);
 59	void (*old_pop)(struct atm_vcc *, struct sk_buff *);
 60	void (*old_release_cb)(struct atm_vcc *);
 61	struct module *old_owner;
 62					/* keep old push/pop for detaching */
 63	enum pppoatm_encaps encaps;
 64	atomic_t inflight;
 65	unsigned long blocked;
 66	int flags;			/* SC_COMP_PROT - compress protocol */
 67	struct ppp_channel chan;	/* interface to generic ppp layer */
 68	struct tasklet_struct wakeup_tasklet;
 69};
 70
 71/*
 72 * We want to allow two packets in the queue. The one that's currently in
 73 * flight, and *one* queued up ready for the ATM device to send immediately
 74 * from its TX done IRQ. We want to be able to use atomic_inc_not_zero(), so
 75 * inflight == -2 represents an empty queue, -1 one packet, and zero means
 76 * there are two packets in the queue.
 77 */
 78#define NONE_INFLIGHT -2
 79
 80#define BLOCKED 0
 81
 82/*
 83 * Header used for LLC Encapsulated PPP (4 bytes) followed by the LCP protocol
 84 * ID (0xC021) used in autodetection
 85 */
 86static const unsigned char pppllc[6] = { 0xFE, 0xFE, 0x03, 0xCF, 0xC0, 0x21 };
 87#define LLC_LEN		(4)
 88
 89static inline struct pppoatm_vcc *atmvcc_to_pvcc(const struct atm_vcc *atmvcc)
 90{
 91	return (struct pppoatm_vcc *) (atmvcc->user_back);
 92}
 93
 94static inline struct pppoatm_vcc *chan_to_pvcc(const struct ppp_channel *chan)
 95{
 96	return (struct pppoatm_vcc *) (chan->private);
 97}
 98
 99/*
100 * We can't do this directly from our _pop handler, since the ppp code
101 * doesn't want to be called in interrupt context, so we do it from
102 * a tasklet
103 */
104static void pppoatm_wakeup_sender(unsigned long arg)
105{
106	ppp_output_wakeup((struct ppp_channel *) arg);
107}
108
109static void pppoatm_release_cb(struct atm_vcc *atmvcc)
110{
111	struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
112
113	/*
114	 * As in pppoatm_pop(), it's safe to clear the BLOCKED bit here because
115	 * the wakeup *can't* race with pppoatm_send(). They both hold the PPP
116	 * channel's ->downl lock. And the potential race with *setting* it,
117	 * which leads to the double-check dance in pppoatm_may_send(), doesn't
118	 * exist here. In the sock_owned_by_user() case in pppoatm_send(), we
119	 * set the BLOCKED bit while the socket is still locked. We know that
120	 * ->release_cb() can't be called until that's done.
121	 */
122	if (test_and_clear_bit(BLOCKED, &pvcc->blocked))
123		tasklet_schedule(&pvcc->wakeup_tasklet);
124	if (pvcc->old_release_cb)
125		pvcc->old_release_cb(atmvcc);
126}
127/*
128 * This gets called every time the ATM card has finished sending our
129 * skb.  The ->old_pop will take care up normal atm flow control,
130 * but we also need to wake up the device if we blocked it
131 */
132static void pppoatm_pop(struct atm_vcc *atmvcc, struct sk_buff *skb)
133{
134	struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
135
136	pvcc->old_pop(atmvcc, skb);
137	atomic_dec(&pvcc->inflight);
138
139	/*
140	 * We always used to run the wakeup tasklet unconditionally here, for
141	 * fear of race conditions where we clear the BLOCKED flag just as we
142	 * refuse another packet in pppoatm_send(). This was quite inefficient.
143	 *
144	 * In fact it's OK. The PPP core will only ever call pppoatm_send()
145	 * while holding the channel->downl lock. And ppp_output_wakeup() as
146	 * called by the tasklet will *also* grab that lock. So even if another
147	 * CPU is in pppoatm_send() right now, the tasklet isn't going to race
148	 * with it. The wakeup *will* happen after the other CPU is safely out
149	 * of pppoatm_send() again.
150	 *
151	 * So if the CPU in pppoatm_send() has already set the BLOCKED bit and
152	 * it about to return, that's fine. We trigger a wakeup which will
153	 * happen later. And if the CPU in pppoatm_send() *hasn't* set the
154	 * BLOCKED bit yet, that's fine too because of the double check in
155	 * pppoatm_may_send() which is commented there.
156	 */
157	if (test_and_clear_bit(BLOCKED, &pvcc->blocked))
158		tasklet_schedule(&pvcc->wakeup_tasklet);
159}
160
161/*
162 * Unbind from PPP - currently we only do this when closing the socket,
163 * but we could put this into an ioctl if need be
164 */
165static void pppoatm_unassign_vcc(struct atm_vcc *atmvcc)
166{
167	struct pppoatm_vcc *pvcc;
168	pvcc = atmvcc_to_pvcc(atmvcc);
169	atmvcc->push = pvcc->old_push;
170	atmvcc->pop = pvcc->old_pop;
171	atmvcc->release_cb = pvcc->old_release_cb;
172	tasklet_kill(&pvcc->wakeup_tasklet);
173	ppp_unregister_channel(&pvcc->chan);
174	atmvcc->user_back = NULL;
175	kfree(pvcc);
176}
177
178/* Called when an AAL5 PDU comes in */
179static void pppoatm_push(struct atm_vcc *atmvcc, struct sk_buff *skb)
180{
181	struct pppoatm_vcc *pvcc = atmvcc_to_pvcc(atmvcc);
182	pr_debug("\n");
183	if (skb == NULL) {			/* VCC was closed */
184		struct module *module;
185
186		pr_debug("removing ATMPPP VCC %p\n", pvcc);
187		module = pvcc->old_owner;
188		pppoatm_unassign_vcc(atmvcc);
189		atmvcc->push(atmvcc, NULL);	/* Pass along bad news */
190		module_put(module);
191		return;
192	}
193	atm_return(atmvcc, skb->truesize);
194	switch (pvcc->encaps) {
195	case e_llc:
196		if (skb->len < LLC_LEN ||
197		    memcmp(skb->data, pppllc, LLC_LEN))
198			goto error;
199		skb_pull(skb, LLC_LEN);
200		break;
201	case e_autodetect:
202		if (pvcc->chan.ppp == NULL) {	/* Not bound yet! */
203			kfree_skb(skb);
204			return;
205		}
206		if (skb->len >= sizeof(pppllc) &&
207		    !memcmp(skb->data, pppllc, sizeof(pppllc))) {
208			pvcc->encaps = e_llc;
209			skb_pull(skb, LLC_LEN);
210			break;
211		}
212		if (skb->len >= (sizeof(pppllc) - LLC_LEN) &&
213		    !memcmp(skb->data, &pppllc[LLC_LEN],
214		    sizeof(pppllc) - LLC_LEN)) {
215			pvcc->encaps = e_vc;
216			pvcc->chan.mtu += LLC_LEN;
217			break;
218		}
219		pr_debug("Couldn't autodetect yet (skb: %6ph)\n", skb->data);
220		goto error;
221	case e_vc:
222		break;
223	}
224	ppp_input(&pvcc->chan, skb);
225	return;
226
227error:
228	kfree_skb(skb);
229	ppp_input_error(&pvcc->chan, 0);
230}
231
232static int pppoatm_may_send(struct pppoatm_vcc *pvcc, int size)
233{
234	/*
235	 * It's not clear that we need to bother with using atm_may_send()
236	 * to check we don't exceed sk->sk_sndbuf. If userspace sets a
237	 * value of sk_sndbuf which is lower than the MTU, we're going to
238	 * block for ever. But the code always did that before we introduced
239	 * the packet count limit, so...
240	 */
241	if (atm_may_send(pvcc->atmvcc, size) &&
242	    atomic_inc_not_zero(&pvcc->inflight))
243		return 1;
244
245	/*
246	 * We use test_and_set_bit() rather than set_bit() here because
247	 * we need to ensure there's a memory barrier after it. The bit
248	 * *must* be set before we do the atomic_inc() on pvcc->inflight.
249	 * There's no smp_mb__after_set_bit(), so it's this or abuse
250	 * smp_mb__after_atomic().
251	 */
252	test_and_set_bit(BLOCKED, &pvcc->blocked);
253
254	/*
255	 * We may have raced with pppoatm_pop(). If it ran for the
256	 * last packet in the queue, *just* before we set the BLOCKED
257	 * bit, then it might never run again and the channel could
258	 * remain permanently blocked. Cope with that race by checking
259	 * *again*. If it did run in that window, we'll have space on
260	 * the queue now and can return success. It's harmless to leave
261	 * the BLOCKED flag set, since it's only used as a trigger to
262	 * run the wakeup tasklet. Another wakeup will never hurt.
263	 * If pppoatm_pop() is running but hasn't got as far as making
264	 * space on the queue yet, then it hasn't checked the BLOCKED
265	 * flag yet either, so we're safe in that case too. It'll issue
266	 * an "immediate" wakeup... where "immediate" actually involves
267	 * taking the PPP channel's ->downl lock, which is held by the
268	 * code path that calls pppoatm_send(), and is thus going to
269	 * wait for us to finish.
270	 */
271	if (atm_may_send(pvcc->atmvcc, size) &&
272	    atomic_inc_not_zero(&pvcc->inflight))
273		return 1;
274
275	return 0;
276}
277/*
278 * Called by the ppp_generic.c to send a packet - returns true if packet
279 * was accepted.  If we return false, then it's our job to call
280 * ppp_output_wakeup(chan) when we're feeling more up to it.
281 * Note that in the ENOMEM case (as opposed to the !atm_may_send case)
282 * we should really drop the packet, but the generic layer doesn't
283 * support this yet.  We just return 'DROP_PACKET' which we actually define
284 * as success, just to be clear what we're really doing.
285 */
286#define DROP_PACKET 1
287static int pppoatm_send(struct ppp_channel *chan, struct sk_buff *skb)
288{
289	struct pppoatm_vcc *pvcc = chan_to_pvcc(chan);
290	struct atm_vcc *vcc;
291	int ret;
292
293	ATM_SKB(skb)->vcc = pvcc->atmvcc;
294	pr_debug("(skb=0x%p, vcc=0x%p)\n", skb, pvcc->atmvcc);
295	if (skb->data[0] == '\0' && (pvcc->flags & SC_COMP_PROT))
296		(void) skb_pull(skb, 1);
297
298	vcc = ATM_SKB(skb)->vcc;
299	bh_lock_sock(sk_atm(vcc));
300	if (sock_owned_by_user(sk_atm(vcc))) {
301		/*
302		 * Needs to happen (and be flushed, hence test_and_) before we unlock
303		 * the socket. It needs to be seen by the time our ->release_cb gets
304		 * called.
305		 */
306		test_and_set_bit(BLOCKED, &pvcc->blocked);
307		goto nospace;
308	}
309	if (test_bit(ATM_VF_RELEASED, &vcc->flags) ||
310	    test_bit(ATM_VF_CLOSE, &vcc->flags) ||
311	    !test_bit(ATM_VF_READY, &vcc->flags)) {
312		bh_unlock_sock(sk_atm(vcc));
313		kfree_skb(skb);
314		return DROP_PACKET;
315	}
316
317	switch (pvcc->encaps) {		/* LLC encapsulation needed */
318	case e_llc:
319		if (skb_headroom(skb) < LLC_LEN) {
320			struct sk_buff *n;
321			n = skb_realloc_headroom(skb, LLC_LEN);
322			if (n != NULL &&
323			    !pppoatm_may_send(pvcc, n->truesize)) {
324				kfree_skb(n);
325				goto nospace;
326			}
327			consume_skb(skb);
328			skb = n;
329			if (skb == NULL) {
330				bh_unlock_sock(sk_atm(vcc));
331				return DROP_PACKET;
332			}
333		} else if (!pppoatm_may_send(pvcc, skb->truesize))
334			goto nospace;
335		memcpy(skb_push(skb, LLC_LEN), pppllc, LLC_LEN);
336		break;
337	case e_vc:
338		if (!pppoatm_may_send(pvcc, skb->truesize))
339			goto nospace;
340		break;
341	case e_autodetect:
342		bh_unlock_sock(sk_atm(vcc));
343		pr_debug("Trying to send without setting encaps!\n");
344		kfree_skb(skb);
345		return 1;
346	}
347
348	atm_account_tx(vcc, skb);
349	pr_debug("atm_skb(%p)->vcc(%p)->dev(%p)\n",
350		 skb, ATM_SKB(skb)->vcc, ATM_SKB(skb)->vcc->dev);
351	ret = ATM_SKB(skb)->vcc->send(ATM_SKB(skb)->vcc, skb)
352	    ? DROP_PACKET : 1;
353	bh_unlock_sock(sk_atm(vcc));
354	return ret;
355nospace:
356	bh_unlock_sock(sk_atm(vcc));
357	/*
358	 * We don't have space to send this SKB now, but we might have
359	 * already applied SC_COMP_PROT compression, so may need to undo
360	 */
361	if ((pvcc->flags & SC_COMP_PROT) && skb_headroom(skb) > 0 &&
362	    skb->data[-1] == '\0')
363		(void) skb_push(skb, 1);
364	return 0;
365}
366
367/* This handles ioctls sent to the /dev/ppp interface */
368static int pppoatm_devppp_ioctl(struct ppp_channel *chan, unsigned int cmd,
369	unsigned long arg)
370{
371	switch (cmd) {
372	case PPPIOCGFLAGS:
373		return put_user(chan_to_pvcc(chan)->flags, (int __user *) arg)
374		    ? -EFAULT : 0;
375	case PPPIOCSFLAGS:
376		return get_user(chan_to_pvcc(chan)->flags, (int __user *) arg)
377		    ? -EFAULT : 0;
378	}
379	return -ENOTTY;
380}
381
382static const struct ppp_channel_ops pppoatm_ops = {
383	.start_xmit = pppoatm_send,
384	.ioctl = pppoatm_devppp_ioctl,
385};
386
387static int pppoatm_assign_vcc(struct atm_vcc *atmvcc, void __user *arg)
388{
389	struct atm_backend_ppp be;
390	struct pppoatm_vcc *pvcc;
391	int err;
392	/*
393	 * Each PPPoATM instance has its own tasklet - this is just a
394	 * prototypical one used to initialize them
395	 */
396	static const DECLARE_TASKLET(tasklet_proto, pppoatm_wakeup_sender, 0);
397	if (copy_from_user(&be, arg, sizeof be))
398		return -EFAULT;
399	if (be.encaps != PPPOATM_ENCAPS_AUTODETECT &&
400	    be.encaps != PPPOATM_ENCAPS_VC && be.encaps != PPPOATM_ENCAPS_LLC)
401		return -EINVAL;
402	pvcc = kzalloc(sizeof(*pvcc), GFP_KERNEL);
403	if (pvcc == NULL)
404		return -ENOMEM;
405	pvcc->atmvcc = atmvcc;
406
407	/* Maximum is zero, so that we can use atomic_inc_not_zero() */
408	atomic_set(&pvcc->inflight, NONE_INFLIGHT);
409	pvcc->old_push = atmvcc->push;
410	pvcc->old_pop = atmvcc->pop;
411	pvcc->old_owner = atmvcc->owner;
412	pvcc->old_release_cb = atmvcc->release_cb;
413	pvcc->encaps = (enum pppoatm_encaps) be.encaps;
414	pvcc->chan.private = pvcc;
415	pvcc->chan.ops = &pppoatm_ops;
416	pvcc->chan.mtu = atmvcc->qos.txtp.max_sdu - PPP_HDRLEN -
417	    (be.encaps == e_vc ? 0 : LLC_LEN);
418	pvcc->wakeup_tasklet = tasklet_proto;
419	pvcc->wakeup_tasklet.data = (unsigned long) &pvcc->chan;
420	err = ppp_register_channel(&pvcc->chan);
421	if (err != 0) {
422		kfree(pvcc);
423		return err;
424	}
425	atmvcc->user_back = pvcc;
426	atmvcc->push = pppoatm_push;
427	atmvcc->pop = pppoatm_pop;
428	atmvcc->release_cb = pppoatm_release_cb;
429	__module_get(THIS_MODULE);
430	atmvcc->owner = THIS_MODULE;
431
432	/* re-process everything received between connection setup and
433	   backend setup */
434	vcc_process_recv_queue(atmvcc);
435	return 0;
436}
437
438/*
439 * This handles ioctls actually performed on our vcc - we must return
440 * -ENOIOCTLCMD for any unrecognized ioctl
441 */
442static int pppoatm_ioctl(struct socket *sock, unsigned int cmd,
443	unsigned long arg)
444{
445	struct atm_vcc *atmvcc = ATM_SD(sock);
446	void __user *argp = (void __user *)arg;
447
448	if (cmd != ATM_SETBACKEND && atmvcc->push != pppoatm_push)
449		return -ENOIOCTLCMD;
450	switch (cmd) {
451	case ATM_SETBACKEND: {
452		atm_backend_t b;
453		if (get_user(b, (atm_backend_t __user *) argp))
454			return -EFAULT;
455		if (b != ATM_BACKEND_PPP)
456			return -ENOIOCTLCMD;
457		if (!capable(CAP_NET_ADMIN))
458			return -EPERM;
459		if (sock->state != SS_CONNECTED)
460			return -EINVAL;
461		return pppoatm_assign_vcc(atmvcc, argp);
462		}
463	case PPPIOCGCHAN:
464		return put_user(ppp_channel_index(&atmvcc_to_pvcc(atmvcc)->
465		    chan), (int __user *) argp) ? -EFAULT : 0;
466	case PPPIOCGUNIT:
467		return put_user(ppp_unit_number(&atmvcc_to_pvcc(atmvcc)->
468		    chan), (int __user *) argp) ? -EFAULT : 0;
469	}
470	return -ENOIOCTLCMD;
471}
472
473static struct atm_ioctl pppoatm_ioctl_ops = {
474	.owner	= THIS_MODULE,
475	.ioctl	= pppoatm_ioctl,
476};
477
478static int __init pppoatm_init(void)
479{
480	register_atm_ioctl(&pppoatm_ioctl_ops);
481	return 0;
482}
483
484static void __exit pppoatm_exit(void)
485{
486	deregister_atm_ioctl(&pppoatm_ioctl_ops);
487}
488
489module_init(pppoatm_init);
490module_exit(pppoatm_exit);
491
492MODULE_AUTHOR("Mitchell Blank Jr <mitch@sfgoth.com>");
493MODULE_DESCRIPTION("RFC2364 PPP over ATM/AAL5");
494MODULE_LICENSE("GPL");